JPH08246200A - Electrolytic production of tin sulfate and bismuth sulfate for tin-bismuth alloy plating - Google Patents

Abstract

PURPOSE: To provide an electrolytic producing method of tin sulfate and bismuth sulfate for tin-bismuth alloy plating. CONSTITUTION: Tin or bismuth is dissolved in a sulfuric acid electrolyte by using an electrolytic cell having an anode and cathode, which are separated by an anion exchange membrane or the anion exchange membrane and a cation exchange membrane, using a sulfuric acid solution as the electrolyte, using tin or bismuth as an anode and impressing DC voltage between the anode and a cathode. As a result, uranium or thorium of radioisotopes is removed and the count number of a radioactive α-particle in a film plated by using the tin or bismuth is suppressed to <=0.1CPH/cm<2> .

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for electrolytically producing tin sulfate and bismuth sulfate for tin-bismuth alloy plating.
As a surface treatment of electronic parts, tin-lead alloy plating is often used, but since the plating bath and the plating film to be obtained contain harmful lead, there is a strong demand for an alternative alloy plating. Thus, the present invention provides a tin-bismuth alloy plating which can replace such a tin-lead alloy plating and is characterized by a radioactive α particle count of less than 0.1 CPH / cm ^2. The present invention relates to a method for electrolytically producing tin sulfate or bismuth sulfate that can be used.

[0002]

2. Description of the Related Art With the recent remarkable development of the electronic industry, tin and solder plating having good solderability have been applied to the electronic parts. Conventionally, a borofluoride bath has been used for solder plating, but fluorine, which is one of the constituent elements of borohydrofluoric acid, is a highly toxic element, and at the same time it is difficult to dispose of the waste liquid. Organic sulfonates, which are less toxic than borofluoric acid salts, have come into widespread use, and there have been reports on plating techniques and additives around these. However, in recent years, when the solder plating is used, since harmful lead is contained in the waste water treatment and the obtained coating, there is a strong demand for tin alloy plating to replace the lead. Corresponding to conventional solder plating (Sn / Pb), tin-bismuth alloy plating, which has similar thermal and mechanical properties such as melting point and solderability, is promising as an alternative alloy to solder plating. Further, tin-lead alloy plating (Sn / Pb = 90/10) mixed with a small amount of lead has been put to practical use as a tin whisker prevention, but tin-containing a small amount of bismuth instead of lead has been used. Bismuth alloy plating (Sn / Bi = 90/10) can prevent tin whiskers as well as the tin-lead alloy.

On the other hand, the steps for producing tin sulfate and bismuth sulfate used in the tin-bismuth alloy plating solution are as follows:
A method of dissolving these metal oxides, chlorides, and hydroxides in sulfuric acid to prepare them has been adopted. However, these oxides, chlorides, and hydroxides contain a large amount of uranium and thorium, which are sources of α-rays, and in such a chemical dissolution method, these impurities are mixed in tin sulfate and bismuth sulfate. However, since a large amount of α-rays are generated from the tin-bismuth alloy electrodeposit after plating, there is the greatest drawback of causing a so-called memory device soft error. In addition, for plating on electronic parts that do not like chloride on the order of several ppm, tin chloride and bismuth sulfate that are usually commercially available inevitably contain chloride.

[0004]

SUMMARY OF THE INVENTION The present invention was devised as a result of repeated studies to provide a tin-bismuth alloy plating solution which suppresses the occurrence of memory errors in semiconductors and replaces chloride-free solder in view of the above circumstances. The radioactive isotopes uranium and thorium contained as unavoidable impurities in Sn and Bi, which are the main components of the film formed by plating, are removed using sulfuric acid, which has no problem in terms of pollution control. The inventors have found a method for producing a tin sulfate or a bismuth sulfate which can provide a tin-bismuth alloy plating capable of suppressing the count number of α particles to 0.1 CPH / cm ² or less, and arrived at the present invention. Therefore, an object of the present invention is to provide an electrolytic production method of tin sulfate or bismuth sulfate, which can provide a tin-bismuth alloy plating film in which the count number of radioactive α particles is reduced. Still another object of the present invention is to provide an electrolytic production method of tin sulfate or bismuth sulfate without chloride contamination.

[0005]

SUMMARY OF THE INVENTION That is, the subject of the present invention is to use an electrolytic cell in which an anode and a cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane, a sulfuric acid solution is used as an electrolytic solution, and a tin is used as an anode. Alternatively, bismuth is used, and a direct current voltage is applied to the anode and the cathode to dissolve tin or bismuth in sulfuric acid electrolyte, and the radioactive α of the film plated with the obtained tin and bismuth salt is used. A method for electrolytic production of tin sulfate or bismuth sulfate for tin-bismuth alloy plating is characterized in that the count number of particles is less than 0.1 CPH / cm ² . Furthermore, the subject of the invention is the tin sulphate and bismuth sulphate salts obtained by the process described above, the tin-bismuth alloy plating baths containing such tin sulphate and bismuth sulphate salts, and the The counted number of radioactive α particles in the formed film is 0.1
In a tin-bismuth alloy-plated electrodeposit having a CPH / cm < ² >.

In the electrolytic production method of the present invention, an electrolytic cell in which an anode and a cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane is used, a sulfuric acid solution is used as an electrolytic solution, and tin or bismuth is used as an anode. And applying a DC voltage to the anode and cathode to electrolyze and dissolve tin or bismuth in the sulfuric acid electrolyte. An example of an electrolysis apparatus that can be used to carry out the electrolytic production method of the present invention is now described in the attached FIG. In FIG. 1, an electrolytic cell 1 for producing tin sulfate and bismuth sulfate.
Is provided with two cathodes 4, for example platinum plates, between which is provided an anode 2, for example tin or bismuth rods, around the anode of which is placed granular tin or bismuth 3 to be melted. Furthermore, an electrolytic cell in which an anion exchange membrane 5 is arranged between the anode 2 and the cathode 4 is used. A shielding film 6 is provided between the anode 2 and the cathode 4 to define an anode chamber and a cathode chamber, respectively. An electrolytic solution 7 made of a sulfuric acid solution is introduced into the anode chamber and the cathode chamber, and stirring and cooling are performed by a circulation pump such as a chemical pump 9 and a heat exchanger 10. A DC power supply 8 is connected to the anode and the cathode. The solution of tin sulfate or bismuth sulfate obtained by electrolysis is taken out from the product take-out port 11.

For the production of tin sulfate and bismuth sulfate containing chlorides of several ppm or less, an electrolytic cell as shown in FIG. 1 in which only an anion exchange membrane is set between an anode chamber and a cathode chamber is used. However, in order to suppress the count of radioactive α particles to 0.1 CPH / cm ² or less, a multilayer electrolytic cell having an anion exchange membrane and a cation exchange membrane set between the anode and the cathode is used. is necessary.

An example of such an electrolytic cell is shown in the attached FIG. In this case, since the shielding plate 6 has a hole with an arbitrary diameter, the electrolytic solution containing tin sulfate or bismuth salt dissolved in the anode chamber passes through the perforated shielding plate 6 and moves to the cathode chamber. can do. A cation exchange membrane 12 is set on the side of the perforated shielding plate 6 in the anode chamber, and tin or bismuth cations can pass through this cation exchange membrane.
On the other hand, an anion exchange membrane 5 is set on the cathode 4 side, and tin or bismuth cations cannot pass through this anion exchange membrane. Then, the produced tin sulfate or bismuth salt-containing solution is taken out from the product take-out port 11.

As conditions for electrolysis according to the present invention, the current density for the membrane is 0.2 to 50 A / dm ² , preferably 5
~ 30 A / dm ² , liquid temperature is 10 ~ 50 ° C, preferably 2
The voltage is 0 to 35 ° C and the voltage is 0.5 to 15V. The electrolytic solution is prepared by diluting commercially available concentrated sulfuric acid with pure water to 5 to 50%, preferably 1
It is 0 to 20%. Further, hydroquinone, resorcinol, pyrocatechol, p-phenolsulfonic acid and cresolsulfonic acid may be added as an antioxidant of tin, and 0.05 to 2.0%, preferably 0.1 to Sn is added. It is 0.5%. The tin and bismuth used as the anode have a quality of 3 nines or more, and the shape is arbitrary, but granular or spherical is preferable. The cathode material is preferably one that is inert to the electrolyte, such as platinum, nickel,
Preference is given to titanium, stainless steel, carbon, or platinum-plated titanium.

The cation exchange membrane and the anion exchange membrane must basically have low electric resistance and good acid resistance, durability and heat resistance. Further, the cation exchange membrane must allow the dissolved tin or bismuth cations to pass from the anode, and the anion exchange membrane must act to prevent the tin or bismuth cations from migrating to the cathode. Although many cation and anion exchange membranes are known today, the preferred cation exchange membranes are those made from polystyrene type or styrene copolymer type resins having strongly acidic groups such as sulfonic acid groups, and are also preferred. The anion exchange membrane is manufactured from a polystyrene type or styrene copolymer type resin having a strongly basic group such as an amino group or a quaternary ammonium group. Here, as a particularly preferable exchange membrane to be used, for example, CMS, C66-10F (cation exchange membrane) manufactured by Tokuyama Soda,
Examples include ACLE-5P and AM-2 (anion exchange membrane).

The reason why the radioactive α particles are reduced in the present invention is that tin or bismuth cations dissolved from the anode remain in the electrolytic solution as they are, but uranium and thorium are dissolved in the electrolytic solution to form an anion complex salt. Formed, so that it does not pass through the cation exchange membrane, only tin or bismuth ions pass through it, while the anion exchange membrane prevents tin or bismuth ions from migrating to the cathode, and as a result It is considered that the solution of tin sulfate or bismuth salt from which uranium and thorium are removed is continuously taken out between the cation exchange membrane and the anion exchange membrane.

Tin sulfate obtained by the electrolytic production method of the present invention
Or bismuth salt is tin or bismuth dissolved in the electrolyte.
It is obtained as a solution of sodium chloride and therefore also contains free sulfuric acid.
Things. In general, the resulting solution will be
Sn²⁺Expressed as 5 to 25% by weight, preferably 10
~ 15 wt% tin sulfate, 5-50 wt%, preferably
An aqueous solution containing 10 to 20% by weight of free sulfuric acid
It In the case of bismuth salt, Bi³⁺Expressed as 5
-25 wt%, preferably 10-15 wt% bisulfate
Mass salt, 5 to 50% by weight, preferably 10 to 20% by weight
It is an aqueous solution containing free sulfuric acid. In this way
The obtained aqueous solution can be directly used for alloy plating.
However, tin and tin are usually used to obtain the desired alloy plating.
The bismuth concentration as well as the free sulfuric acid concentration is regulated. This
The composition of the plating bath can be easily determined by those skilled in the art.
Can be. In addition, the plating bath thus prepared,
Various additives used in tin-bismuth alloy plating baths,
For example, surfactants, brighteners, etc. can be added
It Tin sulfate and bis obtained by the electrolytic production method of the present invention
The plating film obtained from the plating bath containing the mass salt is
The count of radioactive α particles is 0.1 CPH / cm ² 
Is less than.

[0013]

EXAMPLES Next, examples of the present invention will be shown, but the present invention is not limited to these examples, and the above-mentioned tin sulfate having a count of radioactive α particles of 0.1 CPH / cm ² or less and Electrolysis conditions and operating conditions can be arbitrarily changed in accordance with the purpose of obtaining a bismuth sulfate salt.

Example 1 Production of Tin Sulfate This example relates to an electrolytic production process of tin sulfate. The electrolytic cell is made of an acrylic plate with a thickness of 6 mm, and the capacity of the anode chamber is 20.
0 ml, product room 80 ml x 2 rooms, 5 x 16 = 80 cm ²
2 cation exchange membranes (C66-10F), 2 anion exchange membranes (ACLE-5P) at 2.5 mm intervals.
A set of two shielding plates each having a hole of 5 mm was used. Then, a tin rod for contact having a purity of 99.9% and granular tin of 99.9% were also put around the center of the anode, and ^two platinum plating plates on titanium of 0.8 dm ² were used for the cathode. Sulfuric acid was added, and the anolyte flow rate was 3.0 L /
Circulation and cooling were carried out at a flow rate of 1.8 L / min for the cathode at a flow rate of min, and a DC voltage was applied to the anode and the cathode for electrolysis. Table 1 shows the electrolysis conditions and the concentrations of sulfuric acid and tin sulfate in the solutions in the product compartment and the cathode compartment obtained after electrolysis and the dissolution efficiency of Sn.

[Table 1]

Example 2 : Preparation of bismuth sulphate The electrolyzer and operating conditions used in this example are the same as those used in Example 2 above, with 99.9% contact bismuth rod in the anode and the same 99 around it. Granular bismuth (0.9%) was added and electrolysis was performed. Table 2 shows the electrolysis conditions, the concentrations of sulfuric acid and bismuth sulfate in the solutions in the product compartment and the cathode compartment obtained after electrolysis, and the dissolution efficiency of Bi.

[Table 2]

Example 3 Implementation of Tin-Bismuth Alloy Plating Each of these tin sulfate and bismuth sulfate salts taken out from the product chamber of the electrolytic cell used in the above example was dissolved in an aqueous sulfuric acid solution to prepare a suitable surfactant (eg polypropylene). Glycol polyethylene glycol nonyl phenyl ether)
Was added to prepare a tin-bismuth alloy plating bath, and an insoluble anode in which Pt was plated on Ti was used, and a Cu plate was used as a cathode and a DC power source was connected to perform plating. Table 3 below shows the composition of the plating solution (in the composition of the plating solution, the concentrations of tin sulfate and bismuth sulfate are expressed as Sn ²⁺ and Bi ^3+, respectively), the plating conditions, the composition of the electrodeposit and the radioactivity. The count number of α particles is shown.

[Table 3] Comparative bath 1 shown in Table 3 above is a plating bath prepared using commercially available conventional tin sulfate and bismuth sulfate. It can be seen that the number of radioactive α particles in the plating film obtained from this plating solution is very high. On the other hand, in all of the plating baths 1 to 3 according to the present invention, the count of radioactive α particles in the plating film is 0.1.
It can be seen that a low value of less than CPH / cm ² was obtained.

Example 4 Implementation of Tin-Bismuth Alloy Plating Similar to the electrolytic cell used in Example 1 above, except that electrolysis was performed using only an anion exchange membrane between the anode and cathode chambers, each with tin sulfate. And bismuth sulfate salt were produced. Using the tin sulfate and the bismuth sulfate salt thus obtained, a tin-bismuth plating bath was prepared and plated. Composition of plating solution (in the composition of plating solution, the concentrations of tin sulfate and bismuth sulfate are expressed as Sn ²⁺ and Bi ^3+, respectively), plating conditions, composition of electrodeposit and chloride ion in the plating solution The concentrations are shown in Table 4.

[Table 4] Comparative bath 2 shown in Table 4 above is a plating bath prepared using commercially available conventional tin sulfate and bismuth sulfate. The chloride ion in this plating solution was very high, whereas the plating bath 4 according to the present invention had a low chloride ion value.

[0018]

INDUSTRIAL APPLICABILITY The present invention uses an electrolytic cell in which an anode and a cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane, and electrolyzes and dissolves tin and bismuth metal having a quality of 3 nines or more. This provides a method for producing tin sulfate and bismuth sulfate suitable for use in a tin-bismuth alloy plating bath. In the plating bath using the tin sulfate and the bismuth sulfate thus produced, chloride ions were not present, and the number of radioactive α particles counted in the plating film formed from the chloride ion was 0.1 CPH.
/ Cm ^{2 or} less. Therefore, it is possible to form a tin-bismuth alloy plating film that significantly suppresses the occurrence of memory errors without the adverse effect of chloride ions.
It is possible to plate semiconductor device parts such as I, and is also free from lead pollution.

[Brief description of drawings]

FIG. 1 shows one embodiment of an electrolysis device that can be used to carry out the method of the present invention.

FIG. 2 is another embodiment of an electrolysis device that can be used to carry out the method of the present invention.

[Explanation of Codes] 1 Electrolytic cell 2 Tin or bismuth for anode contact 3 Granular tin or bismuth 5 Anion exchange membrane 7 Electrolyte solution 12 Cation exchange membrane

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiaki Okama 21-8 Minami Futami, Futami-cho, Akashi-shi, Hyogo Daiwa Chemical Research Institute Co., Ltd.

Claims (5)

[Claims] 1. An electrolytic cell in which an anode and a cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane is used, a sulfuric acid solution is used as an electrolytic solution, and tin or bismuth is used as an anode. A direct current voltage is applied to the anode and the cathode to dissolve tin or bismuth in a sulfuric acid electrolytic solution, and the count number of radioactive α particles of a film plated with the obtained tin and bismuth salt is 0.1 CPH.
/ Cm ² It is less than / cm ² , The electrolytic production method of tin sulfate or bismuth sulfate for tin-bismuth alloy plating. 2. The method for electrolytically producing tin sulfate or bismuth sulfate according to claim 1, wherein an antioxidant is added to the electrolytic solution. 3. The count number of radioactive α particles of the plating film obtained, which contains tin sulfate and bismuth sulfate obtained by the production method according to claim 1 and free sulfuric acid, and is 0.1.
A tin-bismuth alloy plating bath, which is less than CPH / cm ² . 4. The number of radioactive α particles counted in the plating film obtained from the plating bath according to claim 3 is 0.1 CPH / cm.
A tin-bismuth alloy-plated electrodeposit that is less than ² . 5. A shield plate comprising one anode chamber and two cathode chambers and having holes of arbitrary diameter on both sides of the anode chamber and a cation exchange membrane are set, and an anion exchange membrane is provided on the cathode side of the cathode chamber. Between the system for circulating the electrolytic solution consisting of the sulfuric acid solution respectively set and further introduced into the anode chamber and the cathode chamber, the DC power source connected to the anode and the cathode, and the cation exchange membrane and the anion exchange membrane. An electrolytic apparatus for carrying out the electrolytic production method according to claim 1, characterized in that it has a product take-out port set to.